Non-wetting coating on a fluid ejector

ABSTRACT

A fluid ejector having an inner surface, an outer surface, and an orifice that allows fluid in contact with the inner surface to be ejected. The fluid ejector has a non-wetting monolayer covering at least a portion of the outer surface of the fluid ejector and surrounding an orifice in the fluid ejector. Fabrication of the non-wetting monolayer can include removing a non-wetting monolayer from a second region of a fluid ejector while leaving the non-wetting monolayer on a first region surrounding an orifice in the fluid ejector, or protecting a second region of a fluid ejector from having a non-wetting monolayer formed thereon, wherein the second region does not include a first region surrounding the orifice in the fluid ejector.

CLAIM OF PRIORITY

This application is a continuation of U.S. application Ser. No.11/479,152, filed Jun. 30, 2006, which also claims the benefit of U.S.Provisional Application No. 60/696,035, filed Jul. 1, 2005, the contentsof both are hereby incorporated by reference.

BACKGROUND

This invention relates to coatings on fluid ejectors.

A fluid ejector (e.g., an ink-jet printhead) typically has an interiorsurface, an orifice through which fluid is ejected, and an exteriorsurface. When fluid is ejected from the orifice, the fluid canaccumulate on the exterior surface of the fluid ejector. When fluidaccumulates on the exterior surface adjacent to the orifice, furtherfluid ejected from the orifice can be diverted from an intended path oftravel or blocked entirely by interaction with the accumulated fluid(e.g., due to surface tension). Some materials from which fluid ejectorsare fabricated (e.g., silicon) are hydrophilic, which typicallyexacerbates the problem of accumulation when fluids are ejected.

Non-wetting coatings such as Teflon® and fluorocarbon polymers can beused to coat surfaces. However, Teflon® and fluorocarbon polymerstypically are soft and are not durable coatings. These coatings also canbe expensive and difficult to pattern.

SUMMARY

In one aspect, the invention is directed to a fluid ejector having aninner surface, an outer surface, and an orifice that allows fluid incontact with the inner surface to be ejected. The fluid ejector has anon-wetting monolayer covering at least a portion of an outer surface ofa fluid ejector and surrounding an orifice in the fluid ejector.

Implementations of the invention may include one or more of thefollowing features. The non-wetting monolayer may include moleculeswhich include at least one atom of each of carbon and fluorine. Thenon-wetting monolayer may not cover any portion of an inner surface ofthe fluid ejector.

In another aspect, the invention features a method for forming anon-wetting monolayer on a selected portion a fluid ejector. Anon-wetting monolayer is removed from a second region of a fluid ejectorwhile leaving the non-wetting monolayer on a first region surrounding anorifice in the fluid ejector.

In another aspect, a non-wetting monolayer is formed on a first regionand a second region of a fluid ejector, where the first region surroundsan orifice in the fluid ejector. The non-wetting monolayer is removedfrom the second region while leaving the non-wetting monolayer on thefirst region.

Particular implementations may include one or more of the followingfeatures. The first region may be protected prior to removing thenon-wetting monolayer from the second region. Protecting may includeapplying at least one of tape, photoresist, or wax to the first regionprior to removing the non-wetting monolayer from the second region andremoving the at least one of tape, photoresist, or wax after removingthe non-wetting monolayer. Removing the non-wetting monolayer from thesecond region may include at least one of applying a plasma to thesecond region, laser ablating the second region, or applying ultravioletlight to the second region. The first region may include an outersurface of the fluid ejector and the second region may include an innersurface of the fluid ejector.

In yet another aspect, the invention features a method for forming anon-wetting monolayer on a selected portion of a fluid ejector. A secondregion of a fluid ejector is protected and a non-wetting monolayer isformed on a first region of the fluid ejector, where the first regionsurrounds an orifice in the fluid ejector.

In yet another aspect, a second region of a fluid ejector is protectedfrom having a non-wetting monolayer formed thereon, wherein the secondregion does not include a first region surrounding an orifice in thefluid ejector.

Particular implementations may include one or more of the followingfeatures. The second region may include an interior of the orifice.Protecting the second region may include bonding a silicon substrate tothe fluid ejector. Protecting the second region may include applying atleast one of tape, photoresist, or wax to the fluid ejector prior toforming the non-wetting monolayer and removing the at least one of tape,photoresist, or wax after forming the non-wetting monolayer.

In still another aspect, the invention features a method for forming anon-wetting monolayer on a selected portion of a fluid ejector. Anattachment region is formed on a fluid ejector substrate, where theattachment region includes a first material and the fluid ejectorsubstrate includes a second material. A non-wetting monolayer is formedon the attachment region from a selective precursor, where the selectiveprecursor attaches to the first material and substantially does notattach to the second material.

Particular implementations may include one or more of the followingfeatures. The attachment region may surround an orifice in the fluidejector substrate. The orifice may be formed in the fluid ejectorsubstrate prior to forming the non-wetting monolayer. The selectiveprecursor may include a thiol termination, the first material mayinclude gold, and the second material may include silicon. Forming anattachment region may include sputtering the first material onto thefluid ejector substrate and patterning the first material.

In still another aspect, the invention features a fluid ejector havingan inner surface, an outer surface, and an orifice that allows fluid incontact with the inner surface to be ejected. An attachment regioncovers at least a portion of an outer surface of a fluid ejector andsurrounds an orifice in the fluid ejector, and a non-wetting monolayercovers substantially the entire attachment region and coverssubstantially none of the outer surface of the fluid ejector apart fromthe attachment region.

Particular implementations may include one or more of the followingfeatures. The attachment region may include a first material that issubstantially not present in the outer surface of the fluid ejector. Aprecursor of the non-wetting monolayer may include a thiol termination,the attachment region may include gold atoms, and the outer surface ofthe fluid ejector may include silicon atoms. The attachment region neednot cover any portion of an inner surface of the fluid ejector.

The invention can be implemented to realize one or more of the followingadvantages.

A non-wetting monolayer can reduce the accumulation of fluid on theouter surface of the fluid ejector. The monolayer can be durable and canbe insoluble in most solvents, allowing multiple types of inks to beused with the fluid ejector. Coating material can be saved because ofthe thinness of the monolayer. Wet processes are not required afteretching the fluid ejector, and therefore residue associated with a wetprocess can be avoided.

If the non-wetting monolayer is removed post-deposition, the coating canbe deposited without first protecting or masking regions of a substrate.If the underlying layer is masked before deposition of the coating, thenprocessing steps to remove undesired regions of a non-wetting monolayercan be eliminated. A non-wetting monolayer can be deposited easily andaccurately in desired regions on a substrate.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A-1B are cross-sectional views of implementations of an uncoatedfluid ejector.

FIG. 1C is a cross-sectional view of an implementation of the fluidejector from FIG. 1B with a non-wetting coating on an outer surface.

FIG. 2 is a bottom view of the fluid ejector from FIG. 1C.

FIG. 3 is a cross-sectional view of a second implementation of a fluidejector with a non-wetting coating on an outer surface.

FIG. 4 is a cross-sectional view of a nozzle layer coated with anon-wetting coating.

FIG. 5 is a cross-sectional view of a nozzle layer with protective tapeon an outer surface.

FIG. 6 is a cross-sectional view of a nozzle layer.

FIGS. 7A-7D illustrate process steps in one implementation of a methodfor forming a non-wetting coating on a nozzle layer.

FIGS. 8A-8C illustrate process steps in a second implementation of amethod for forming a non-wetting coating on a nozzle layer.

FIGS. 9A-9B illustrate process steps in a third implementation of amethod for forming a non-wetting coating on a nozzle layer.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1A is a cross-sectional view of an uncoated fluid ejector 100(e.g., an ink-jet printhead nozzle), which can be constructed asdescribed in U.S. patent application Ser. No. 10/913,571, the contentsof which are hereby incorporated by reference. The uncoated fluidejector 100 includes a flow-path module 110 and a nozzle layer 120, bothof which can be made of silicon (e.g., single crystal silicon). In oneimplementation, the uncoated fluid ejector 100 is a single unit, and theflow-path module 110 and the nozzle layer 120 are not separate pieces.The uncoated fluid ejector 100 includes an inner surface 150 and anouter surface 160. A membrane layer 182 is positioned above a pumpingchamber 135. An actuator 172 pressurizes fluid (e.g., an ink, forexample, a water-based ink) in the pumping chamber 135 and the fluidflows through a descender 130 and is ejected through an orifice 140 inthe nozzle layer 120. The actuator 172 can include a piezoelectric layer176, a lower electrode 178 (e.g., a ground electrode), and an upperelectrode 174 (e.g., a drive electrode). The membrane layer 182 and theactuator 172 are not shown in the following figures, but can be present.

As shown in FIG. 1B, the uncoated fluid ejector 100 optionally caninclude an inorganic layer 165 formed on the nozzle layer 120, in whichcase the outer surface 160 of the uncoated ejector can be considered theouter surface of the inorganic layer 165. The inorganic layer 165 is alayer of a material, such as SiO₂, that promotes adhesion of anon-wetting coating. In one implementation, the inorganic seed layer 165is a native oxide layer (such a native oxide typically has a thicknessof 1 to 3 nm). In another implementation, the inorganic layer is adeposited seed layer. For example, an inorganic seed layer 165 of SiO₂can be formed on the nozzle layer 120, for example, by introducing SiCl₄and water vapor into a chemical vapor deposition (CVD) reactorcontaining the uncoated fluid ejector 100. A valve between the CVDchamber and a vacuum pump is closed after pumping down the chamber, andvapors of SiCl₄ and H₂O are introduced into the chamber. The partialpressure of the SiCl₄ can be between 0.05 and 40 Torr (e.g., 0.1 to 5Torr), and the partial pressure of the H₂O can be between 0.05 and 20Torr (e.g., 0.2 to 10 Torr). The deposition temperature is typicallybetween room temperature and 100 degrees centigrade. Alternatively, theinorganic seed layer 165 can be sputtered onto the nozzle layer 120. Thesurface to be coated by the inorganic seed layer 165 can be cleaned(e.g., by applying an oxygen plasma) before forming the inorganic seedlayer 165.

The thickness of the seed layer can be, for example, 5 nm to 100 nm. Forsome fluids to be ejected, the performance can be affected by thethickness of the inorganic layer. For example, for some “difficult”fluids, a thicker layer, e.g., 30 nm or more, such as 40 nm or more, forexample 50 nm or more, will provide improved performance. Such“difficult” fluids can include, for example, PEDOT and Light EmittingPolymer.

One implementation of a fabrication process alternates between applyinglayers of the seed material and forming layers the non-wetting coating.In this case, the individual seed layers can be, for example, 5 to 20 nmthick. The exposed surfaces of the device can be cleaned (e.g., byapplying an oxygen plasma) before forming the layer of seed material.Hypothetically, this fabrication process could result in a layer stackwith alternating layers of seed material and non-wetting coating.However, without being limited to any particular theory, under someconditions the cleaning process might remove the immediately previouslydeposited non-wetting coating, such that the resulting device has asingle continuous thick seed layer (rather than alternating layers ofoxide and non-wetting coating).

Another implementation of the fabrication process simply deposits theentire seed layer in a single continuous step to provide a unitary,monolithic seed layer.

Referring to FIGS. 1B and 1C, a non-wetting coating 170, such as aself-assembled monolayer that includes a single molecular layer, isapplied to the outer surface 160 of the uncoated fluid ejector 100 toform a coated fluid ejector 105. The non-wetting coating 170 can beapplied using vapor deposition, rather than being brushed, rolled, orspun on. The outer surface of the fluid ejector can be cleaned (e.g., byapplying an oxygen plasma) before applying the non-wetting coating 170.In one implementation, the inner surface 150, the descender 130, and theinner surface of orifice 140 are not coated in the final fluid ejectorproduct. The non-wetting coating 170 can be deposited on the outersurface 160 of the uncoated fluid ejector 100, for example, byintroducing a precursor and water vapor into the CVD reactor at a lowpressure. The partial pressure of the precursor can be between 0.05 and1 Torr (e.g., 0.1 to 0.5 Torr), and the partial pressure of the H₂O canbe between 0.05 and 20 Torr (e.g., 0.1 to 2 Torr). The depositiontemperature can be between room temperature and 100 degrees centigrade.The coating process and the formation of the inorganic seed layer 165can be performed, by way of example, using a Molecular Vapor Deposition(MVD)™ machine from Applied MicroStructures, Inc.

Suitable precursors for the non-wetting coating 170 include, by way ofexample, precursors containing molecules that include a non-wettingtermination and a termination that can attach to a surface of the fluidejector. For example, precursor molecules that include a carbon chainterminated at one end with a —CF₃ group and at a second end with an—SiCl₃ group can be used. Specific examples of suitable precursors thatattach to silicon surfaces includetridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS). Without being limitedby any particular theory, it is believed that when a precursor (such asFOTS or FDTS) whose molecules include an —SiCl₃ termination areintroduced into the CVD reactor with water vapor, silicon atoms from the—SiCl₃ groups bond with oxygen atoms from —OH groups on the inorganicseed layer 165 or on a native oxide of the nozzle layer 120.

In another implementation, the coated fluid ejector 105 does not includethe inorganic seed layer 165, and the non-wetting coating 170 is applieddirectly to the nozzle layer 120. In this case, the outer surface 160 ofthe uncoated ejector can be considered the outer surface of the nozzlelayer 120.

FIG. 2 shows a bottom view of the coated fluid ejector 105. The orifice140 is shown as a rectangular opening, though other opening geometriesmay be suitable, such as a circle or a polygon with five or more sides.

As shown in FIG. 3, multiple layers of a non-wetting coating 370 can beapplied to the outer surface 360 of a fluid ejector 300. The multiplelayers can be applied by repeatedly performing the deposition stepsdescribed in the context of FIGS. 1B. In one implementation,fluorocarbon chains of a non-wetting coating are cut to expose siliconatoms or —CH₂ groups before depositing a layer of the non-wettingcoating 370. Fluorocarbon chains can be cut (etched) by an oxygen plasmatreatment. An inductively coupled plasma (ICP) source is used togenerate active oxygen radicals, and the radicals etch the fluorocarbonchains of the non-wetting coating. The oxygen can be introduced into aCVD reactor, for example, at a pressure of 0.4 Torr and a with a flowrate of 260 sccm. RF power from the ICP source can be applied at 200 Wfor 30 seconds.

Referring again to FIGS. 1B and 1C, the non-wetting coating 170 can bedeposited on the outer surface 160 of the uncoated fluid ejector beforeor after the flow-path module 110 and the nozzle layer 120 are joinedand before or after the orifice 140 is formed in the nozzle layer 120.When the orifice 140 is formed after depositing the non-wetting coating170, the non-wetting coating 170 typically should be masked while theorifice 140 is being formed to prevent damage to the non-wetting coating170. If the non-wetting coating 170 is applied after the orifice 140 isformed, non-wetting coating that is deposited on the inner surface 150of the coated fluid ejector 105 can be removed while leaving thenon-wetting coating deposited on the outer surface 160. The orifice 140can also be masked during the application of non-wetting coating 170 sothat substantially no non-wetting coating is deposited on the innersurface 150.

It can be advantageous to apply the non-wetting coating 170 afterforming one or more orifices (e.g., orifice 140) in the nozzle layer120. FIG. 4 shows a nozzle layer 420 to which a non-wetting coating 470(e.g., a non-wetting monolayer) has been applied before the nozzle layer420 was joined to a flow-path module. The non-wetting coating 470typically coats all exposed surfaces of the nozzle layer 420 whenapplied using a CVD process. The non-wetting coating 470 coats both aninner surface 450 and an outer surface 460 of the nozzle layer 420. Aninorganic layer (e.g., inorganic seed layer 165 in FIG. 1B or nativeoxide) can be present on nozzle layer 420, but is not shown in FIG. 4for the sake of clarity.

It can be advantageous for selected regions of the nozzle layer 420 notto be covered with a non-wetting coating. Therefore, non-wetting coatingcan be removed from the selected regions. For example, the non-wettingcoating 470 can be removed from the inner surface 450 of the nozzlelayer 420. As shown in FIG. 5, a masking layer 580 (e.g., tape) can beapplied over the non-wetting coating 470 on the outer surface 460 ofnozzle layer 420, and the masked nozzle layer can be placed on a solidsurface, such as a silicon substrate 590. An etchant (e.g., oxygenplasma) can be applied to the inner surface 450 of the nozzle layer 420to remove the portion of the non-wetting coating 470 on the innersurface 450. As shown in FIG. 6, the silicon substrate 590 and themasking layer 580 can be removed after applying the etchant, leaving thenozzle layer 420 with the non-wetting coating 470 only on the outersurface 460.

Alternatively, light (e.g., ultraviolet (UV), deep UV, or green lightfrom a laser) can be used to remove non-wetting coating from selectedregions. For example, referring again to FIG. 4, light can be used toirradiate the inner surface 450 of the nozzle layer 420 to remove theportion of the non-wetting coating 470 on the inner surface 450. Thelight can be supplied, for example, by laser such as an excimer laser(e.g., an ArF or KrF excimer laser). The nozzle layer 420 can be tiltedrelative to the source of the light so that the walls of orifice 440 areirradiated.

After removing the non-wetting coating 470 from the inner surface 450,the nozzle layer 420 can be attached to a flow-path module (e.g.,flow-path module 110 in FIG. 1A). The methods discussed here can also beused when the non-wetting coating 470 is applied after the nozzle layer420 is attached to the flow-path module. For example, an etchant can beapplied to the inner surface 450 through a descender (e.g., descender130 in FIG. 1A) in the flow-path module. One method of applying anetchant through the descender is to connect an ozone generator to aninlet port of the assembled fluid ejector and supply ozone (e.g., at a2% or greater concentration in oxygen gas or in a mixture of oxygen andnitrogen) to the descender and the inner surface 450 through the inletport. The outer surface 460 can be protected with tape while the ozoneis supplied to the descender and the inner surface 450. In addition, theozone can be heated (e.g., to above 80 degrees centigrade, for example,to 120 degrees centigrade) before being injected into descender. In analternative implementation, oxygen plasma can be used instead of ozone.

As an alternative to removing non-wetting coating from selected regions,the non-wetting coating can be prevented from forming in the selectedregions. For example, the non-wetting coating 470 can be prevented fromforming on the inner surface 450 of the nozzle layer 420 during adeposition step. Another alternative is to allow the non-wetting coatingto form in the selected regions and deposit a layer of material (e.g.,SiO₂) on top of the non-wetting coating to make the selected regionhydrophilic.

As shown in FIG. 7A, a protective structure 785 can be formed for aregion (e.g., orifice 740) on a nozzle layer 720. The protectivestructure 785 can be formed on a silicon substrate 795, for example, byforming a region of silicon oxide 787 over the protective structure 785and etching the silicon substrate 795 using inductively-coupled plasmato form raised regions.

As shown in FIG. 7B, the nozzle layer 720 and the protective siliconsubstrate 795 can be placed in contact or bonded, thereby masking theregion, in this case the orifice 740, with the protective structure 785.As shown in FIG. 7C, vapor deposition can be used to apply a non-wettingcoating 770 to the areas on the outer surface 760 of the nozzle layer720 that are not masked by the protective structure 785. FIG. 7D showsthe nozzle layer 720 after the silicon substrate 795 has been removed,leaving non-wetting coating 770 on the outer surface 760 of nozzle layer720 in the regions that were not covered by the protective structure785.

Certain precursors for non-wetting coatings selectively attach tocertain materials, while substantially not attaching to other materials.For example, a thiol-terminated precursor attaches to gold, butsubstantially does not attach to silicon. A precursor with a selectivetermination and a non-wetting termination can be used to control theregions in which a non-wetting coating forms on a substrate (e.g.,silicon). For example, as shown in FIG. 8A, an oxide layer 810optionally is patterned on a silicon substrate 820. In FIG. 8B, amaterial (e.g., gold) to which a selective precursor attaches issputtered onto the silicon substrate 820 or onto the oxide layer 810, ifpresent, and is patterned (e.g., using photoresist) into an attachmentregion 830. FIG. 8C shows the silicon substrate 820 after an orifice 840has been etched (e.g., using inductively-coupled plasma) and anon-wetting coating 870 has been formed using a selective precursor(e.g., a thiol-terminated precursor) that attaches to the attachmentregion 830, but not to the oxide layer 810 or the silicon substrate 820.

Alternatively, as shown in FIG. 9A, the material to which the selectiveprecursor attaches is sputtered directly onto a silicon substrate 920and is patterned into an attachment region 930. FIG. 9B shows thesilicon substrate 920 after an orifice 940 has been etched and anon-wetting coating 970 has been formed using the selective precursor.

Various methods can be used to mask regions of a nozzle layer where anon-wetting coating is not desired before depositing the non-wettingcoating. Masking can also be used to protect regions of a non-wettingcoating when portions of the non-wetting coating are removed afterdeposition. For example, tape, wax, or photoresist can be used as a maskto prevent the non-wetting coating from being deposited in selectedregions of the nozzle layer. The tape, wax, or photoresist can beremoved after the non-wetting coating has been deposited on the nozzlelayer. Likewise, tape, wax, or photoresist can be applied over selectedregions of a non-wetting coating to prevent the removal of thenon-wetting coating in those regions during processing steps that occurafter the deposition of the non-wetting coating.

A selected region of a non-wetting coating can be removed withoutremoving the entire non-wetting coating by laser ablation using a hardmask or using a servo-controlled laser. A selected region of anon-wetting coating can also be removed by etching the non-wettingcoating with plasma while protecting, using a mask (e.g., photoresist)for example, the regions of the non-wetting coating that are not to beremoved. UV light can also be used to remove selected regions of anon-wetting coating, and regions not to be removed can be protected witha mask (e.g., a metal contact mask).

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, method steps may be performed in a different order and stillproduce desirable results. Accordingly, other embodiments are within thescope of the following claims.

1. A method for forming a non wetting layer on a selected portion of afluid ejector, the method comprising: applying a protective structure toan outer surface of a fluid ejector, the fluid ejector including anozzle defined by an opening in the outer surface and an inner surfaceextending upstream from the opening, wherein the protective structure isapplied to the outer surface downstream of the opening and masks aregion of the outer surface including the opening; forming a non-wettinglayer on an unmasked region of the outer surface of the fluid ejector.2. The method of claim 1, wherein forming the non-wetting layercomprises applying the non-wetting layer from downstream of the opening.3. The method of claim 1, wherein the protective structure comprises abody and projections extending from the body, and wherein theprojections contact the outer surface.
 4. The method of claim 3, whereinapplying the non-wetting layer comprises dispensing a precursor betweenthe body of the protective structure and the outer surface of the fluidejector.
 5. The method of claim 1, wherein the non-wetting layer is asingle molecular layer.
 6. The method of claim 1, wherein the protectivestructure comprises a silicon substrate and masking the region includesbonding the silicon substrate to the fluid ejector.
 7. The method ofclaim 1, further comprising removing the protective structure afterforming the non-wetting layer.
 8. The method of claim 1, wherein theprotective structure contacts a portion of the outer surface surroundingthe opening of the orifice.
 9. The method of claim 1, wherein formingthe non-wetting layer comprises applying a precursor onto the fluidejector.
 10. The method of claim 9, wherein a precursor includes a thioltermination.
 11. The method of claim 9, wherein the precursor comprisestridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane or1H,1H,2H,2H-perfluorodecyltrichlorosilane.
 12. The method of claim 9,wherein the precursor is applied using a chemical vapor depositionreactor.
 13. The method of claim 1, wherein the non-wetting layercomprises molecules that include at least one atom of each of carbon andfluorine.
 14. The method of claim 1, wherein the non-wetting layercomprises fluorocarbon chains.
 15. The method of claim 1, whereinforming the non-wetting layer comprises forming a self-assemblednon-wetting layer.
 16. The method of claim 1, further comprising formingan inorganic seed layer on the fluid ejector before forming thenon-wetting layer.
 17. The method of claim 1, wherein forming thenon-wetting layer comprises repeatedly forming single molecule layers ontop of one another.
 18. The method of claim 1, wherein the non-wettinglayer is formed on substantially all portions of the outer surface apartfrom a contacting region of the protective structure and the outersurface.